U.S. patent application number 11/073510 was filed with the patent office on 2005-08-11 for non-aqueous electrolyte secondary battery.
Invention is credited to Hara, Fumiko, Kameyama, Fumito, Komiyama, Michiko, Sugiyama, Tsuyoshi.
Application Number | 20050175891 11/073510 |
Document ID | / |
Family ID | 27342987 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050175891 |
Kind Code |
A1 |
Kameyama, Fumito ; et
al. |
August 11, 2005 |
Non-aqueous electrolyte secondary battery
Abstract
A non-aqueous electrolyte secondary battery has a positive
electrode having a positive electrode collector, on which a
positive electrode active material layer containing a positive
electrode active material as a complex oxide of Li and transition
metals are formed, and a negative electrode having a negative
collector, on which a negative electrode active material layer is
formed. The non-aqueous electrolyte secondary battery is a gel or
solid non-aqueous electrolyte secondary battery having a battery
device in which a positive electrode and a negative electrode are
laminated with an electrolyte layer therebetween in a film-state
packaging member constructed by metal foil laminated films, and
containing a lithium salt, a non-aqueous solvent, and a polymer
material. The concentration in mass ratio of a free acid in the
electrolyte layer is 60 ppm and less. Average particle diameter of
the positive electrode active material lies in a range from 10 to
22 .mu.m, the minimum particle diameter is 5 .mu.m or larger, the
maximum particle diameter is 50 .mu.m or smaller, and specific
surface of the positive electrode active material is 0.25 m.sup.2/g
or smaller. Lithium carbonate (Li.sub.2CO.sub.3) contained in the
positive electrode active material is 0.15 percent by weight and
less. Moisture contained in the positive electrode active material
is 300 ppm and less.
Inventors: |
Kameyama, Fumito;
(Fukushima, JP) ; Hara, Fumiko; (Fukushima,
JP) ; Sugiyama, Tsuyoshi; (Miyagi, JP) ;
Komiyama, Michiko; (Fukushima, JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080
WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Family ID: |
27342987 |
Appl. No.: |
11/073510 |
Filed: |
March 7, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11073510 |
Mar 7, 2005 |
|
|
|
09825988 |
Apr 4, 2001 |
|
|
|
Current U.S.
Class: |
429/163 ;
429/185; 429/223; 429/224; 429/231.3; 429/316; 429/317 |
Current CPC
Class: |
H01M 6/10 20130101; H01M
2300/0085 20130101; H01M 4/62 20130101; H01M 10/0565 20130101; H01M
50/124 20210101; H01M 2004/021 20130101; H01M 4/1393 20130101; H01M
4/02 20130101; H01M 4/525 20130101; H01M 10/4235 20130101; H01M
10/0567 20130101; H01M 10/0587 20130101; H01M 4/131 20130101; H01M
10/0525 20130101; Y02E 60/10 20130101; H01M 4/505 20130101; H01M
4/1391 20130101; H01M 50/116 20210101; H01M 2300/0082 20130101;
H01M 4/133 20130101; H01M 50/557 20210101; H01M 6/168 20130101 |
Class at
Publication: |
429/163 ;
429/185; 429/231.3; 429/223; 429/224; 429/317; 429/316 |
International
Class: |
H01M 002/00; H01M
002/08; H01M 004/50; H01M 004/52; H01M 010/40 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2000 |
JP |
P2000-102624 |
Apr 10, 2000 |
JP |
P2000-108412 |
Apr 12, 2000 |
JP |
P2000-111044 |
Claims
1-22. (canceled)
1. A non-aqueous electrolyte secondary battery comprising: a
battery device having a positive electrode having a collector, on
which a positive electrode active material layer containing a
positive electrode material is formed, a negative electrode, and a
non-aqueous electrolyte layer, the battery device being sealed in a
film-state packaging member, wherein: concentration in mass ratio
of a free acid in the electrolyte layer is 60 ppm and less; the
electrolyte is made of a lithium salt and a polymer compound, in
which the lithium salt is dissolved or mixed, and one or more
polymer compounds selected from one or more polymer compounds
selected from the group consisting of ether-based polymers which is
poly(ethylene oxide) and a crosslinked of the poly(ethylene oxide),
poly(methacrylate) ester polymer, acrylate polymer, and fluorine
polymer which is poly(vinylidene fluoride) and poly(vinylidene
fluoride-co-hexafluoropropylene).
Description
RELATED APPLICATION DATA
[0001] The present application claims priority to Japanese
Applications Nos. P2000-102624 filed Apr. 4, 2000, P2000-108412
filed Apr. 10, 2000, and P2000-111044 filed Apr. 12, 2000, which
applications are incorporated herein by reference to the extent
permitted by law.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a battery in which a
battery device having electrolyte as well as a positive electrode
and a negative electrode is sealed in a film-state packaging
member.
[0003] In recent years, a secondary battery used as a power source
of a portable electronic device has been actively studied and
developed. Among the secondary batteries, attention is paid on a
lithium secondary battery and a lithium ion secondary battery as
secondary batteries capable of realizing high energy density.
Conventionally, each of each secondary batteries is generally
constructed by interposing a liquid electrolyte (hereinbelow, also
called electrolyte solution) obtained by dissolving a lithium salt
into a nonaqueous solvent between a positive electrode and a
negative electrode and accommodating them in a housing made of a
metal.
[0004] When a hard case cell made of a metal is used, a problem
such that strong recent demands of a lighter, smaller, and thinner
secondary battery are not sufficiently addressed occurs. As
electronic devices are becoming smaller and smaller, a secondary
battery is also demanded to have an increased degree of freedom in
shape. When a metal hard case cell is used, the demand regarding
shape cannot be also sufficiently addressed.
[0005] In order to prevent leakage of the electrolyte solution, it
is necessary to use a metal hard case cell (a positive electrode
cover and a negative electrode can) having rigidity. As described
above, when the non-aqueous solution is used, a problem such as
leakage occurs. It is therefore proposed to use, in place of the
electrolyte solution, a gel electrolyte obtained by making a
non-aqueous electrolyte solution containing a lithium salt held by
a polymer compound, a solid electrolyte obtained by dispersing or
mixing a lithium salt into a polymer compound having ion
conductivity, or an electrolyte in which a lithium salt is held by
a solid inorganic conductor. This non-aqueous gel polymer secondary
battery has a positive electrode having a positive electrode
collector on which a positive electrode active material layer is
formed, and a negative electrode having a negative electrode
collector on which a negative electrode active material is formed
and has a structure that a gel layer containing an electrolyte is
sandwiched between the positive electrode active material layer of
the positive electrode and the negative electrode active layer of
the negative electrode.
[0006] In the gel layer containing the electrolyte in such a
non-aqueous gel polymer secondary battery, an electrolyte solution
is held in a gel matrix. By using the gel or solid electrolyte, the
problem of leakage of the electrolyte solution is solved. The hard
case cell becomes unnecessary. The degree of freedom in shape can
be increased by using a film more flexible than a metal housing or
the like as a packaging member. Further reduction in size, weight,
and thickness can be realized.
[0007] In the case of using a film-state case such as a laminated
film, a polymer film, or a metal film obtained by covering metal
foil made of aluminum or the like with a resin as a packaging
member, however, when lithium hexafluorophosphate (LiPF.sub.6),
lithium tetrafluoroboric acid (LiBF.sub.4), or the like is used as
a lithium salt, a problem such as a battery expansion occurs. One
of the factors of this phenomenon may be considered that, even if a
very small amount of moisture exists in a battery system, a lithium
salt is descomposed and a free acid component such as hydrogen
fluoride (HF) or ion fluoride is generated. When the free acid
component reacts with the lithium to form lithium fluoride (LiF) or
the like and the lithium in the battery system is consumed,
problems such that shelf stability or charge/discharge cycle
characteristic deteriorates and a theoretical battery capacity
cannot be obtained, occur.
[0008] In a conventional secondary battery using non-aqueous gel
electrolyte or solid electrolyte, lithium-cobalt complex oxide is
used as a positive electrode active material. A secondary battery
using a non-aqueous gel electrolyte or solid electrolyte housed in
a metal foil laminate case has a significant challenge to suppress
expansion which is seen in a high temperature storage test or the
like since a housing for accommodating the aluminum laminate pack
may be broken due to the expansion.
[0009] In a conventional non-aqueous lithium ion secondary battery,
the positive electrode active material contains from 0.8% to 1.2%
of lithium. carbonate (Li.sub.2CO.sub.3) so as to provide the
function of generating CO.sub.2 gas to shut down a safety valve in
the case where the temperature of the battery becomes high when
heated or excessively charged. A conventionally used positive
electrode active material includes about 500 ppm of water content
by which a gas is generated when the battery is heated or
excessively charged.
[0010] On the other hand, a non-aqueous gel polymer secondary
battery has improved safety against heating and excessive charging,
and it is unnecessary to generate a gas when the temperature
becomes high. The conventional non-aqueous gel polymer secondary
battery uses lithium-cobalt complex oxide as a positive electrode
active material. A non-aqueous gel polymer secondary battery using
a metal foil laminate pack obtained by covering metal foil such as
aluminum foil with a resin has a significant challenge to suppress
expansion, which is seen in a high temperature storage test or the
like since there is the possibility that an aluminum laminate pack
is not housed in a set case due to the expansion.
SUMMARY OF THE INVENTION
[0011] The invention has been achieved in consideration of the
problems and its object is to provide a battery capable of
suppressing shape change and suppressing deterioration in battery
characteristics.
[0012] Another object of the invention is to provide a positive
electrode active material capable of suppressing expansion of a
battery and a non-aqueous electrolyte secondary battery using the
positive electrode active material.
[0013] According to first aspect of the invention, a non-aqueous
electrolyte secondary battery includes a battery device having a
positive electrode having a collector, on which a positive
electrode active material layer containing a positive electrode
material is formed, a negative electrode, and an electrolyte layer,
the battery device being sealed in a film-state packaging member,
and concentration in mass ratio of a free acid in the electrolyte
layer is 60 ppm and less. In the battery, more preferably, the
positive electrode active material is a composite oxide
LiC.sub.OO.sub.2.
[0014] As the packaging member, preferably, a metal foil laminate
case or laminated film obtained by coating metal foil with a resin
and having the structure of packaging resin layer/metal
layer/sealant layer is used.
[0015] According to the second aspect of the invention, a
non-aqueous electrolyte secondary battery comprises a positive
electrode having a positive electrode collector on which a positive
electrode active material layer containing a positive electrode
material is formed, a negative electrode having a negative
electrode collector on which a negative electrode active material
layer is formed, and a film-state case as a packaging member. In
the battery, average particle diameter of the positive electrode
active material lies in a range from 10 to 22 .mu.m.
[0016] More preferably, the positive electrode active material has
minimum particle diameter of 5 .mu.m or larger, maximum particle
diameter of 50 .mu.m and less, and specific surface area of 0.25
m.sup.2/g and less. Preferably, the positive electrode active
material is LiC.sub.OO.sub.2.
[0017] According to a third aspect of the invention, a non-aqueous
electrolyte secondary battery comprises a positive electrode having
a positive electrode collector, on which a positive electrode
active material layer containing a positive electrode material is
formed, a negative electrode having a negative electrode collector
on which a negative electrode active material layer is formed, and
a film-state case as a packaging member. In the battery, the
positive electrode active material layer contains 0.15 percent by
weight of carbonate compound. Preferably, moisture contained in the
positive electrode active material is 300 ppm and less. Preferably,
the positive electrode active material layer is made of a lithium
and a transition metal complex oxide LiMO.sub.2 (where, M is at
least one material selected from Co, Ni, and Mn. More preferably,
the positive electrode active material layer is made of
LiCoO.sub.2, and the carbonate contained in the positive electrode
active material is LiCoO.sub.3.
[0018] In the non-aqueous electrolyte secondary battery according
to the first aspect of the invention, since the concentration in
mass ratio of a free acid in the electrolyte is 60 ppm and less,
even when the film-state packaging member is used, a change in
shape is suppressed, and deterioration in battery characteristics
is suppressed.
[0019] In the non-aqueous electrolyte secondary battery according
to the second aspect of the invention, since the average particle
diameter of the positive electrode active material lines in a range
from 10 to 22 .mu.m, the specific surface area of the positive
electrode active material becomes narrow, a reaction area decreases
and, as a result, generation of gas when the battery is stored at
high temperature, is suppressed.
[0020] In the non-aqueous electrolyte secondary battery according
to the third aspect of the invention, since the carbonate contained
in the positive electrode active material is 0.15 percent by weight
and less, decomposing reaction when the battery is stored at high
temperature is suppressed, and generation of gas is suppressed.
[0021] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a perspective view showing the configuration of a
secondary battery according to the first aspect of the
invention;
[0023] FIG. 2 is an exploded perspective view of the secondary
battery shown in FIG. 1;
[0024] FIG. 3 is a cross section taken along a III-III line of a
battery device shown in FIG. 2;
[0025] FIG. 4 is a characteristic diagram showing concentration of
a free acid in each of electrolytes of examples and comparative
examples;
[0026] FIG. 5 is a characteristic diagram showing discharge
capacity of a secondary battery in each of examples and comparative
examples; and
[0027] FIG. 6 is a perspective view showing the configuration of a
non-aqueous electrolyte secondary battery according to second and
third aspects of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Embodiments of the invention will be described in detail
hereinbelow with reference to the drawings.
[0029] FIG. 1 shows the appearance of a secondary battery according
to an embodiment of the invention. FIG. 2 is an exploded view of
the secondary battery shown in FIG. 1. In the secondary battery, a
battery device 20 to which a positive electrode lead 11 and a
negative electrode lead 12 are attached is sealed in a film-state
packaging member 30 (film-state case such as a laminated film in
which metal foil such as aluminum foil and the like is coated with
a resin, a polymer film, or a metal film).
[0030] FIG. 3 is a cross section taken along a III-III line of a
sectional structure of the battery device 20 in FIG. 2.
[0031] The battery device 20 is a obtained by laminating a positive
electrode 21 and a negative electrode 22 with, for example, a
gel-state electrolyte layer 23 and a separator 24 in-between and
rolling the laminated body. The outermost peripheral portion of the
negative electrode 22 is protected by a protection tape 25.
[0032] The positive electrode 21 has, for example, a positive
electrode collector layer 21a and a positive electrode mixture
layer 21b which is provided on one side or both sides of the
positive electrode collector layer 21a. The positive electrode
mixture layer 21b is not provided at one of the ends in the
longitudinal direction of the positive electrode collector layer
21a, and there is a portion where the positive electrode collector
layer 21a is exposed. The positive electrode lead 11 is attached to
the exposed portion.
[0033] The positive electrode collector layer 21a is made of metal
foil such as aluminum (Al) foil, nickel (Ni) foil, or stainless
steel foil. The positive electrode mixture layer 21b contains, for
example, a positive electrode material, a conducting agent such as
carbon black or graphite, and a binder such as polyvinylidene
fluoride. Preferable positive electrode materials are, for example,
a metallic oxide, a metallic sulfide, and a specific polymer
material. One or more of the materials is/are selected according
the application of the battery. To increase energy density, the
most preferable material is a lithium composite oxide containing
LixMO2 as a main component. In the composition formula, M denotes
one or more kinds of transition metal(s). Particularly, at least
one of cobalt (Co), nickel (Ni), and manganese (Mn) is preferable.
The value (x) varies according to a charge/discharge state of the
battery and usually satisfies 0.05.ltoreq.x.ltoreq.1.12. Examples
of such lithium composite oxide are LiNiyCo1-yO.sub.2 (where,
0.ltoreq.y.ltoreq.1) and LiMn.sub.2O.sub.4.
[0034] The negative electrode 22 has, for example, in a manner
similar to the positive electrode 21, a negative electrode
collector layer 22a and a negative a positive electrode mixture
layer 21b which is provided on one side or both sides of the
negative electrode collector layer 22a. The negative electrode
mixture layer 22b is not provided at one of the ends in the
longitudinal direction of the negative electrode collector layer
22a, and there is a portion where the negative electrode collector
layer 22a is exposed. The negative electrode lead 12 is attached to
the exposed portion.
[0035] The negative electrode collector layer 22a is made of metal
foil such as copper (Cu) foil, nickel foil, or stainless steel
foil. The negative electrode mixture layer 22b contains, for
example, one or more of negative electrode materials capable of
occluding and releasing a lithium metal or lithium.
[0036] Negative electrode materials capable of occluding and
releasing lithium are metals and semiconductors each can form an
alloy or compound with lithium, and alloys and compounds of the
metals and semiconductors. Each of the metals, alloys, and
compounds is expressed by the chemical formula DsEtLiu. In the
chemical formula, D denotes at least one of a metal element and a
semiconductor element capable of forming an alloy or compound with
lithium, and E denotes at least one of a metal element and a
semiconductor element other than lithium and D. Each of values s,
t, and u satisfies s>0, t.gtoreq.0, and u.gtoreq.0.
[0037] Among the metal or semiconductor elements each can form an
alloy or compound with lithium, Group 4B metal and semiconductor
elements are preferable. More preferable elements are silicon and
tin, and the most preferable element is silicon. Alloys and
compounds of those elements are also preferable. Examples of the
alloys and compounds are SiB.sub.4, SiB.sub.6, Mg.sub.2Si,
Mg.sub.2Sn, Ni.sub.2Si, TiSi.sub.2, MoSi.sub.2, CoSi.sub.2,
NiSi.sub.2, CaSi.sub.2, CrSi.sub.2, Cu.sub.5Si, FeSi.sub.2,
MnSi.sub.2, NbSi.sub.2, TaSi.sub.2, VSi.sub.2, WSi.sub.2, and
ZnSi.sub.2.
[0038] Other examples of negative electrode materials capable of
occluding and releasing lithium are carbonaceous materials, metal
oxides and polymer materials. Examples of the carbonaceous
materials are pyrocarbons, cokes, graphites, glassy carbons,
polymer organic compound calcined materials, carbon fiber, and
activated carbon. The cokes include pitch coke, needle coke, and
petroleum coke. The polymeric compound calcined material is a
material obtained by calcining a polymeric material such as
phynolic resin or furan resin at an appropriate temperature so as
to be carbonated. As a metal oxide, tin oxide (SiO.sub.2) or the
like can be mentioned. Examples of the polymeric materials are
polyacetylene, and polypyrrole.
[0039] The electrolyte layer 23 is composed by, for example, a
lithium salt, a non-aqueous solvent for dissolving the lithium
salt, and a polymer material. Proper lithium salts are LiPF.sub.6,
LiBF.sub.4, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N- , LiC.sub.4F.sub.9SO.sub.3, LiCl and
LiBr. Two or more of them may be mixed.
[0040] Appropriate non-aqueous solvents are, for example, ethylene
carbonate, propylene carbonate, butylene carbonate, vinylene
carbonate, .gamma.-butyrolactone, .gamma.-valerolactone,
diethoxyethan, tetraphydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolane, methyl acetate, methyl propionic acid, dimethyl
carbonate, diethyl carbonate, methyl ethyl carbonate,
2,4-difluoroanisole, 2,6-difluoroanisole, and 4-bromoveratrole. Two
or more kinds of the above materials may be mixed. In the case of
using a laminated film which will be described hereinlater as the
packaging member 30, preferably, any of the materials boiling at
150.degree. C. or higher such as ethylene carbonate, propylene
carbonate, butylene carbonate, .gamma.-butyrolactone,
2,4-difluoroanisole, 2,6-difluoroanisole, and 4-bromoveratrole is
used. When the material is easily vaporized, the packaging member
30 is expanded and the outer shape deteriorates.
[0041] Appropriate polymer materials are, for example,
fluoride-contained polymers such as polyvinylidene fluoride and
poly(vinylidene fluoride-co-hexafluoropropylene), ether-contained
polymers such as polyacrylonitrile, acrylonitrile-butadiene rubber,
acrylonitrile-butadien-styren resin, acrylonitrile polyethylene
chloride diene styrene resin, acrylonitrile vinyl chloride resin,
acrylonitrile methacrylate resin, acrylonitrile acrylate resin, and
polyethylen oxide, and crosslinkers of the ethyl-contained
polymers, and polyethyl modified siloxane. Two or more materials
may be mixed. Copolymers with the following materials may be also
used; acrylonitrile, vinyl acetate, methyl methacrylate, butyl
methacrylate, methyl acrylate, butyl acrylate, itaconic acid,
methyl acrylate hydroxide, ethyl acrylate hydroxide, acryl amide,
vinyl chloride, and vinylidene fluoride. Further, copolymers with
ethylene oxide, propylene oxide, methyl methacrylate, butyl
methacrylate, methyl acrylate, and butyl acrylate may be also used.
A copolymer of vinylidene fluoride and hexafluoropropylene, and a
copolymer of ethyl modified siloxane may be used. More preferably,
it is made by a micro porous polyolefin film.
[0042] The separator 24 is made by, for example, a porous film made
of a polyolefin-based material such as polypropylene or
polyethylene or a porous film made of an inorganic material such as
ceramic nonwoven cloth. A structure in which two or more kinds of
porous films are stacked, may be also used. More preferably, it is
made by a micro porous polyolefin film.
[0043] The positive electrode lead 11 and the negative electrode
lead 12 are led from the inside of the packaging member 30 to the
outside, for example, in the same direction. A part of the positive
electrode lead 11 is connected to an exposed portion in the
positive electrode collector layer 21a in the packaging member 30.
A part of the negative electrode lead 12 is connected to an exposed
portion of the negative electrode collector layer 22a in the
packaging member 30. The positive electrode lead 11 and the
negative electrode lead 12 are made of a metal material such as
aluminum, copper, nickel, or stainless steel in a thin film or mesh
state.
[0044] In the case of using a film-state case as the packaging
member 30, the packaging member 30 is constructed by, for example,
two rectangular films 30a and 30b each having a thickness of about
90 .mu.m to 110 .mu.m. For example, the peripheral portions of the
films 30a and 30b adheres to each other by fusion or by using an
adhesive. When the packaging member 30 (films 30a and 30b) takes
the form of a laminated film obtained by coating metal foil such as
aluminum foil with a resin, the following materials can be used.
Plastic materials to be used will be abbreviated as follows:
polyethylene terephthalate:PET, fused polypropylane:PP, casting
polypropylene:CPP, polyethylene:PE, low-density polyethylene:LDPE,
high-density polyethylene:HDPE, linear low-density
polyethylene:LLDPE, and nylon:Ny. Aluminum as a metal material used
for a permeability-resistant barrier film is abbreviated as AL. SUS
foil may be used in the same way.
[0045] The most common structure is an packaging layer/metal
layer/sealant layer=PET/AL/PE. Not only the combination but also
configurations of other general laminated films as shown below can
be also used; packaging layer/metal film/sealant layer=Ny/AL/CPP,
PET/AL/CPP, PET/AL/PET/CPP, PET/Ny/AL/CPP, PET/Ny/AL/Ny/CPP,
PET/Ny/AL/Ny/PE, Ny/PE/AL/LLDPE, PET/PE/AL/PET/LDPE, and
PET/Ny/AL/LDPE/CPP. Obviously, the metal film can be also made of
any of metals other than AL.
[0046] In the embodiment, a laminated film in which, for example, a
nylon film, aluminum foil, and a polyethylene film are laminated in
this order, is used. In the laminated film, the polyethylene film
faces the battery device 20. The aluminum foil in the laminated
film has moisture resistance for preventing intrusion of outside
air. In place of the laminated film, a laminated film having the
other structure, a polymer film made of polypropylene or the like,
or a metal film can be also used as the packaging member 30.
[0047] As shown in FIGS. 2 and 3, the positive electrode lead 11,
the negative electrode lead 12, and the packaging member 30 closely
adheres to each other with, for example, a film 31 in-between so as
to prevent intrusion of the outside air. The film 31 is made of a
material which adheres to the positive electrode lead 11 and the
negative electrode lead 12. When each of the positive electrode
lead 11 and the negative electrode lead 12 is made of any of the
above-described metal materials, preferably, the film 31 is made of
a polyolefin resin such as polyethylene, polypropylene, modified
polyethylene, or modified polypropylene.
[0048] A non-aqueous electrolyte secondary battery having such a
structure can be manufactured as follows.
[0049] First, a positive electrode mixture is prepared by mixing a
positive electrode material, a conducting agent, and a binder. The
positive electrode mixture is dispersed in a solvent of
N-methyl-pyrrolidone or the like to thereby obtain a positive
electrode mixture slurry. The positive electrode mixture slurry is
applied on one side or both sides of the positive electrode
collector layer 21a, dried, and compression molded, thereby forming
the positive electrode mixture layer 21b. In such a manner, the
positive electrode 21 is fabricated. The positive electrode mixture
is not applied to one end of the positive electrode collector layer
21a but the end is exposed.
[0050] Next, a negative electrode mixture is prepared by mixing a
negative electrode material capable of occluding and releasing
lithium with a binder and dispersing the mixture in a solvent of
N-methyl-pyrrolidone or the like to thereby obtain a negative
electrode mixture slurry. The negative electrode mixture slurry is
applied on one side or both sides of the negative electrode
collector layer 22a, dried, and compression molded, thereby forming
the negative electrode mixture layer 21b. In such a manner, the
negative electrode 21 is fabricated. The negative electrode mixture
is not applied to one end of the negative electrode collector layer
22a but the end is exposed.
[0051] Subsequently, the positive electrode lead 11 is attached to
the exposed portion of the positive electrode collector layer 21a
by resistance welding, ultrasonic welding, or the like, and the
electrolyte is, for example, applied on the positive electrode
mixture layer 21b to form the electrolyte layer 23. The negative
electrode lead 12 is attached to the exposed portion of the
negative electrode collector layer 22a by electric resistance
welding, ultrasonic welding, or the like, and the electrolyte is,
for example, applied on the negative electrode mixture layer 22b to
form the electrolyte layer 23. After that, for example, the
separator 24, the positive electrode 21 on which the electrolyte
layer 23 is formed, the separator 24, and the negative electrode 22
on which the electrolyte layer 23 is formed are sequentially
laminated and a laminated product is rolled, and the outermost
portion is, for example, adhered by the protection tape 25. In such
a manner, the battery device 20 is formed.
[0052] At the time of forming the electrolyte layer 23, for
example, the materials (that is, the mixture of the lithium salt,
non-aqueous solvent, and polymer material) of the electrolyte
stored in a dry atmosphere are heated to about 70.degree. C. to be
polymerized. While maintaining the temperature, the resultant is
applied on the positive electrode mixture layer 21b or the negative
electrode mixture layer 22b, thereby preventing generation of a
free acid.
[0053] After forming the battery device 20, for example, the films
30a and 30b are prepared to sandwich the battery device 20 and are
contact bonded to the battery device 20 in a reduced pressure
atmosphere, and the outer peripheral portions of the films 30a and
30b are bonded to each other by thermal fusion bonding or the like.
Films 31 are disposed so as to sandwich the positive electrode lead
11 and the negative electrode lead 12 at the end portions of the
films 30a and 30b from which the positive electrode lead 11 and the
negative electrode lead 12 are led, and the peripheries of the
films 30a and 30b are bonded to each other via the film 31. In such
a manner, the battery shown in FIGS. 1 to 3 is completed.
[0054] The secondary battery acts as follows.
[0055] When the secondary battery is charged, for example, lithium
ions are released from the positive electrode 21 and occluded by
the negative electrode 22 via the electrolyte layer 23. When the
secondary battery is discharged, for example, the lithium ions are
released from the negative electrode 22 and occluded by the
positive electrode 21 with the electrolyte layer 23 in-between.
Since the concentration in mass ratio of a free acid in the
electrolyte layer 23 is 60 ppm and less, the battery is prevented
from being expanded. The reaction between the free acid and the
lithium in the battery system is suppressed, so that excellent
battery characteristics are attained.
[0056] In the embodiment, the concentration in mass ratio of the
free acid in the electrolyte layer 23, that is, electrolyte is 60
ppm and less. The free acid denotes an acid generated when the
lithium salt is decomposed, and ions generated when the acid is
dissociated. The free acid is generated due to decomposition of the
lithium salt, for example, when moisture exists or when the
electrolyte is heated. Specifically, hydrogen fluoride, fluoride
ion, hydrogen chloride (HCl), chloride ion (Cl--), hydrogen bromide
(HBr), bromide ion (Br--), and the like can be mentioned. In the
secondary battery, by suppressing the concentration of the free
acid, generation of a gaseous hydride such as hydrogen fluoride gas
and generation of a gas by corrosion reaction in the battery is
suppressed, and the expansion of the battery is therefore
prevented. Consumption of the lithium due to reaction between the
free acid and the lithium is also suppressed, and an increase in
internal resistance due to generation of lithium fluoride is also
prevented.
[0057] As described above, in the secondary battery according to
the embodiment, the concentration in mass ratio of the free acid in
the electrolyte is suppressed to 60 ppm and less. Thus, generation
of a gaseous hydride in the battery and generation of gas by
corrosion reaction in the battery can be suppressed. Consequently,
a change in shape due to expansion can be prevented with the
film-state packaging member 30. In the case where the battery is
stored in high-temperature environment, the shape can be
maintained.
[0058] The consumption of lithium due to the reaction between the
free acid and the lithium in the battery system can be also
suppressed, and an increase in the internal resistance due to
generation of lithium fluoride can be prevented. Thus, various
battery characteristics such as capacity characteristic, shelf
stability, and charge/discharge cycle can be prevented from
deterioration.
[0059] A method of manufacturing a non-aqueous electrolyte
secondary battery having non-aqueous gel electrolyte according to
the invention will now be described. First, a positive electrode is
fabricated by forming a positive electrode active material layer on
a positive electrode collector. While heating the positive
electrode to a temperature exceeding room temperature, a gel layer
containing electrolyte is formed on the positive electrode active
material layer of the positive electrode.
[0060] The gel layer containing electrolyte may be applied on one
side or on each of both sides by a single-side coater.
Specifically, the electrode unwound from the wound role is heated
by an electrode preheater. On the electrode active material layer
on one side of the electrode, a composition for forming the gel
layer containing electrolyte is applied from the coater head. The
applied composition for forming the gel layer containing
electrolyte is dried when passed through a dryer and becomes a gel
layer containing electrolyte. The electrode on which the gel layer
containing electrolyte is formed, is taken up by the wound
role.
[0061] The gel layer containing electrolyte can be also
simultaneously coated on both sides by a double-side coater. The
electrode unwound from the wound role is heated by the electrode
preheater, and a composition for forming the gel layer containing
electrolyte is applied from the coater head simultaneously on both
sides of the electrode active material layer. The applied
composition for forming the gel layer containing electrolyte is
dried when passed through a dryer and becomes a gel layer
containing electrolyte. The electrode on which the gel layer
containing electrolyte is formed, is taken up by the wound
role.
[0062] When pressing is necessary, for example, after forming the
electrode active material layer and before forming the gel layer
containing the electrolyte, the electrode can be pressed by a
general press roller.
[0063] In a manner similar to the case of fabricating the positive
electrode, by forming a negative electrode active layer on the
negative electrode collector, the negative electrode is fabricated.
Subsequently, while heating the negative electrode to a temperature
exceeding the room temperature, a gel layer containing electrolyte
solution is formed on a negative electrode active layer of the
negative electrode.
[0064] The gel layer containing electrolyte on the positive
electrode side and that on the negative electrode side adheres to
each other, thereby obtaining an electrode body.
[0065] The obtained electrode body may be assembled to thereby
achieving a completed battery by any of methods such as; a method
of forming a slit in the electrode on which the gel layer
containing electrolyte is formed and assembling the electrode; a
method of forming a slit in the electrode first, forming the gel
layer containing the electrolyte solution, and assembling the
electrode; and a method as a combination of the methods, of forming
the gel layer containing the electrolyte solution and forming a
slit in one of the electrodes, forming a slit and then forming the
gel layer containing the electrolyte solution on the other
electrode, and assembling the electrodes. A method of forming the
gel layer containing electrolyte only one side of an electrode,
forming a slit, forming the gel layer on the other face of the
electrode, and assembling the electrode may be also used.
[0066] In the battery device, after leads are welded to the
portions in the collector, in which the active material layer is
not applied, the electrodes are laminated so that the active
material layers of the electrodes face each other. The electrodes
may be laminated by stacking electrodes which are cut in a desired
size, winding stacked electrodes, and the like.
[0067] The battery device fabricated in such a manner is sandwiched
by the laminated films, the resultant is pressed to increase the
adhesion of the gel layers containing electrolyte on both
electrodes and is sealed, so that the battery device is not exposed
to outside air. In such a manner, a non-aqueous gel polymer
secondary battery using the aluminum laminate pack as shown in FIG.
1 is obtained.
[0068] The invention is not limited to the method of preheating the
electrode before coating the composition for forming the gel layer
containing electrolyte in the invention. A method of passing a
temperature-controlled roll, a method of blowing
temperature-controlled air, a method of providing an infrared ray
lamp, or the like can be mentioned.
EXAMPLE
[0069] Further, examples of the invention will be described in
detail.
Examples 1-1 to 1-31
[0070] First, a copolymer of vinylidene fluoride and
hexafluoropropylene as polymer materials was dissolved in a solvent
obtained by mixing propylene carbonate and ethylene carbonate, and
further, LiPF.sub.6 was dissolved as a lithium salt. The mixing
ratio in volume of the solvent and the polymeter material,
specifically, propylene carbonate:ethylene carbonate:copolymer was
set to 4:4:1. LiPF.sub.6 was dissolved at the rate of 0.74
mol/dm.sup.3.
[0071] The mixture solution was stored in a drying chamber for one
week or longer and heated to about 70.degree. C. so as to be
gelled. In such a manner, electrolytes of the Examples 1-1 to 1-31
were obtained. The electrolytes of the Examples 1-1 to 1-31 were
fabricated separately under the same conditions.
[0072] The concentration of the free acid (hydrogen fluoride in
this case) of the obtained electrolyte was measured. To be
specific, the electrolyte is dissolved in cold water of 1.5.degree.
C. or lower so as not to be hydrolyzed. After adding bromothymol
blue as an indicator, acid-bace neutrization titration was carried
out by using a sodium hydroxide (NaOH) solution of 0.01
mol/dm.sup.3, thereby measuring the concentration. The results are
shown in FIG. 4. In FIG. 4, the vertical axis denotes concentration
(unit: ppm) in mass ratio of the free acid, and the lateral axis
denotes numbers of the example and comparative examples which will
be described hereinlater. As shown in FIG. 4, the concentration in
mass ratio of the free acid in each of the electrolytes of the
examples is 60 ppm and less.
[0073] As Comparative Examples 1-1 to 1-29 of the present examples,
electrolytes were fabricated in a manner similar to the examples
except that the storage time in the dying chamber was set to one
day and the heating temperature was set to 80 to 90.degree. C. The
concentration of the free acid was measured with respect to each of
Comparative Examples 1-1 to 1-29 in a manner similar to the
examples. The result is also shown in FIG. 4. As shown in FIG. 4,
the concentration at mass ratio of the free acid in each of the
electrolytes in Comparative Examples 1-1 to 1-29 was 70 ppm or
higher.
[0074] Secondary batteries as shown in FIGS. 1 to 3 were fabricated
by using the electrolytes of the examples and comparative examples.
First, a positive electrode mixture was prepared by mixing
lithium-cobalt complex oxide (LiCoO.sub.2) as a positive electrode
material, graphite as a conducting agent, and polyvinylidene
fluoride as a binder. The positive electrode mixture was dispersed
in N-methyl-pyrrolidone as a solvent to thereby obtain a positive
electrode mixture slurry. The positive electrode mixture slurry was
applied on both sides of the positive electrode collector layer 21a
made of aluminum foil, dried, and compression molded, thereby
forming the positive electrode mixture layer 21b. In such a manner,
the positive electrode 21 was fabricated. A negative electrode
mixture was prepared by mixing graphite powders as a negative
electrode material with polyvinylidene fluoride as a binder, the
mixture was dispersed in a solvent of N-methyl-pyrrolidone to
thereby obtain a negative electrode mixture slurry. The negative
electrode mixture slurry was applied on both sides of the negative
electrode collector layer 22a made of copper foil, dried, and
compression molded, thereby forming the negative electrode mixture
layer 22b. In such a manner, the negative electrode 22 was
fabricated.
[0075] After forming the positive and negative electrodes, the
positive electrode lead 11 was attached to the positive electrode
collector layer 21a and the electrolyte was applied on the positive
electrode mixture layer 21b to form the electrolyte layer 23. The
negative electrode lead 12 was attached to the negative electrode
collector layer 22a and the electrolyte was applied on the negative
electrode mixture layer 22b to form the electrolyte layer 23. After
that, a porous polypropylene film as the separator 24 was prepared,
and the separator 24, the positive electrode 21, the separator 24,
and the negative electrode 22 were sequentially laminated and a
laminated product was rolled. The outermost portion was adhered by
the protection tape 25. In such a manner, the battery device 20 was
formed.
[0076] After forming the battery device 20, two metal foil
laminated films each obtained by laminating a nylon film, aluminum
foil, and a polyethylene film in this order were prepared, and the
battery device 20 was sandwiched by the metal foil laminated films
so that the film 31 for improving the adhesion was disposed at the
end portions from which the positive electrode lead 11 and the
negative electrode lead 12 were led. After that, the laminated
films were contact bonded to the battery device 20, and the
peripheries of the metal foil laminated films were fusion bonded to
each other, thereby obtaining a secondary battery having a length
of 62 mm, a width of 35 mm, and a thickness of about 3.8 mm.
[0077] Each of the secondary batteries of examples and comparative
examples were repeatedly charged and discharged, a change in shape
after the charging was examined, and an initial discharge capacity
was measured. The charging was performed with a constant current of
250 mA until the battery voltage reaches 4.2V and then by a
constant voltage of 4.2V until the total charging time reached nine
hours. On the other hand, the discharging was performed with a
constant current of 250 mA until the battery voltage reaches
3V.
[0078] As a result, a change in the shape of the battery after
charging was hardly seen in each of the secondary batteries of
Examples 1-1 to 1-31. On the other hand, in the secondary battery
of Comparative Examples 1-1 to 1-29, a gas is generated between the
packaging member 30 and the battery device 20 or in the battery
device 20 in almost all of them. Each of the secondary batteries
was expanded to a thickness of about 4.0 mm to 4.4 mm.
[0079] FIG. 5 shows the results of the initial discharge capacity.
In FIG. 5, the vertical axis denotes discharge capacity (unit;
mAh), and the vertical axis denotes numbers of the examples and the
comparative examples. As understood from FIG. 5, the discharge
capacity larger than 565 mAh was obtained in each of Examples 1-1
to 1-31. In contrast, the discharge capacity smaller than 535 mAh
was obtained in each of Comparative Examples 1-1 to 1-20. When they
are compared with each other by using the average values, the
average value of the examples is 586 mAh and that of the
comparative examples is 512 mAh. In the examples, the discharge
capacity larger than that in the comparative examples by 14.5% was
obtained. Variations in the values in the examples are smaller than
those in the comparative examples. Thus, stable results were
derived.
[0080] Further, each of the secondary batteries in the examples and
the comparative examples was charged and discharged for 100 cycles.
The ratio of the discharge capacity in the 100.sup.th cycle to that
in the 1.sup.st cycle (that is, the capacity sustain ratio in the
100.sup.th cycle) was calculated. As a result, the average value of
the capacity sustain ratio of Examples 1-1 to 1-31 is 95%. On the
other hand, the average value of the capacity sustain ratio of the
comparative examples is 87%, which is lower than the average value
of the examples.
[0081] That is, it was found that, in fabrication of the
electrolyte, after sufficiently drying the lithium salt, solvent,
and polymer material, the electrolyte is gelled at low temperature
of about 70.degree. C., the concentration of the free acid in the
electrolyte can be suppressed to 60 ppm or lower at the mass ratio,
a change in shape of the battery can be effectively prevented, and
stable and excellent capacity characteristics and charge/discharge
cycle characteristics can be obtained.
Examples 2-1 to 2-3
[0082] As Examples 2-1 to 2-3, secondary batteries were fabricated
in a manner similar to Examples 1-1 to 1-31 except that the
concentration in mass ratio of the free acid in the electrolyte was
changed as shown in Table 1. As Comparative Examples 2-1 to 2-3 of
Examples 2-1 to 2-3, secondary batteries were fabricated in a
manner similar to the examples except that the concentration of the
free acid in the electrolyte as shown in Table 1.
1 TABLE 1 concentration initial capacity in mass ratio discharge
sustain of free acid capacity ratio change in (ppm) (mAh) (%) shape
Example 2-1 25 582 95 hardly occurs Example 2-2 50 584 95 hardly
occurs Example 2-3 60 571 93 hardly occurs Comparative 100 511 89
expanded Example 2-1 Comparative 200 494 84 expanded Example 2-2
Comparative 400 481 81 expanded Example 2-3
[0083] The concentration of the free acid in the electrolyte in
each of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3 was
controlled by adjusting the drying time in the drying chamber and
the gelling temperature. Specifically, in Example 2-1, the drying
time was set as one week and the gelling temperature was set as
70.degree. C. In Example 2-2, the drying time was set as 5 days,
and the gelling temperature was set as 70.degree. C. In Example
2-3, the drying time was set as 5 days, and the gelling temperature
was set as 75.degree. C. In Comparative Example 2-1, the drying
time was set as one day, and the gelling temperature was set as
80.degree. C. to 90.degree. C. In Comparative Example 2-2, there is
no drying time, and the gelling temperature was set as 85.degree.
C. to 95.degree. C. In Comparative Example 2-3, there is no drying
time, and the gelling temperature was set as 95.degree. C. to
105.degree. C.
[0084] With respect to the secondary batteries of Examples 2-1 to
2-3 and Comparative Examples 2-1 to 2-3, a change in shape after
charging, initial discharge capacity, and capacity sustain ratio in
the 100.sup.th cycle were measured in a manner similar to Examples
1-1 to 1-31. Table 1 shows the results. As understood from Table 1,
when the concentration of the free acid in the electrolyte is
suppressed to 60 ppm in mass ratio, a change in shape of the
battery can be prevented and excellent capacity characteristic and
charge/discharge characteristic can be achieved.
[0085] A second aspect of the invention will now be described.
Obviously, the invention is not limited to the following
examples.
Example 3
[0086] (Fabrication of Positive Electrode)
[0087] Suspension of the following composition of a positive
electrode active material layer was mixed by a disper for four
hours and was coated in a pattern on both sides of aluminum foil
having a thickness of 20 .mu.m. The coating pattern includes a
coated portion having a length of 160 mm and an uncoated portion
having a length of 30 mm, which are repeatedly provided on both
sides. The start and end positions of coating on both sides were
controlled to coincide with each other.
2 Composition of positive electrode active material layer parts by
weight LiCoO.sub.2 100 polyvinylidene fluoride 5 (average molecular
weight: 300,000) carbon black (average particle diameter: 15 nm) 10
N-methyl-2-pyrrolidone 100
[0088] LiCoO.sub.2 has, as shown in Table 2, average particle
diameter of 10 .mu.m, the minimum particle diameter of 5 .mu.m, the
maximum particle diameter of 18 .mu.m, and specific surface area of
0.25 m2/g.
3TABLE 2 Particle size distribution and specific surface area of
positive electrode active material average particle minimum
diameter particle minimum (50% diameter particle particle (5%
particle diameter Specific diameter) diameter) (95% particle
surface area .mu.m .mu.m diameter) .mu.m m.sup.2/g Example 3 10 5
18 0.25 Example 4 16 7 40 0.23 Example 5 22 9 50 0.21 Comparative 6
3 12 0.51 Example 3 Comparative 8 5 16 0.38 Example 4
[0089] The row film of which both sides are coated with the
positive electrode, was pressed with linear pressure of 300 kg/cm.
After the press, the thickness of the positive electrode was 100
.mu.m and the density of the positive electrode active material
layer was 3.45 g/cc.
[0090] (Fabrication of Negative Electrode)
[0091] Suspension of the following composition of a positive
electrode active material layer was mixed by a disper for four
hours and was coated in a pattern on both sides of copper foil
having a thickness of 10 .mu.m. The coating pattern includes a
coated portion having a length of 160 mm and an uncoated portion
having a length of 30 mm, which are repeatedly provided on both
sides. The start and end positions of coating on both sides were
controlled to coincide with each other.
4 Composition of negative electrode active material layer parts by
weight artificial graphite 100 (average particle diameter: 20
.mu.m) polyvinylidene fluoride 15 (average molecular weight:
300,000) N-methyl-2-pyrrolidone 200
[0092] The row sheet of which both sides are coated with the
negative electrode was pressed with linear pressure of 300 kg/cm.
After the press, the thickness of the negative electrode was 90
.mu.m and the density of the negative electrode active material
layer was 1.30 g/cc.
[0093] Formation of Gel Layer Containing Electrolyte Solution
[0094] The composition for forming the gel layer containing the
electrolyte solution was mixed by a disper for one hour in a heated
state at 70.degree. C. and was coated in a pattern on the negative
electrode active material layers on both sides of the negative
electrode collector so as to have a thickness of 20 .mu.m and was
coated in a pattern on the positive electrode collector active
material layers on both sides of the positive electrode collector
so as to have a thickness of 20 .mu.m. A dryer was controlled so
that only dimethyl carbonate evaporates substantially.
5 Composition for forming gel layer parts containing electrolyte
solution by weight poly(hexafluoropropylene-vinylidene fluoride)
copolymer *1 5 dimethyl carbonate (DMC) 75 electrolyte solution
(LiPF6: 1.2 mole/litter) *2 20 *1: content of hexafluoropropylene =
6 parts by weight *2: solvents used for electrolyte solution:
ethylene carbonate (EC)/propylene carbonate
(PC)/.gamma.-butyrolactone (GBL) = 4/3/3
[0095] At the time of forming the gel layer containing electrolyte
solution, the positive and negative electrodes were heated by
setting an electrode preheater at a predetermined temperature
60.degree. C.
[0096] The row negative electrode on which the gel layer containing
the electrolyte solution was cut into 40 mm width to fabricate a
band-shaped pancake. The row positive electrode was cut into 38 mm
width to fabricate a band-shaped electrode pancake.
[0097] (Fabrication of Battery)
[0098] After that, the leads were welded to both the positive and
negative electrodes, and the positive and negative electrodes were
adhered to each other so that their electrode active material
layers were in contact with each other and contact-bonded. The
resultant was sent to an assembling section where the battery
device was formed. The battery device was sandwiched so as to be
covered with the laminated films. By welding the laminated films,
the non-aqueous gel polymer secondary battery as shown in FIG. 6
was fabricated. As described above, the non-aqueous gel polymer
secondary battery of the embodiment used an aluminum laminate pack.
The laminated film was obtained by stacking nylon, aluminum, and
casting polypropylene (CPP) in accordance with the order from the
outside. The thickness of nylon was 30 .mu.m, that of aluminum was
40 .mu.m, and that of CPP was 30 .mu.m. The thickness of the whole
stack layers was 100 .mu.m.
Example 4
[0099] This example is similar to Example 3 except that physical
properties of the positive electrode active material were
different. Specifically, LiCoO.sub.2 as the positive electrode
active material has, as shown in Table 2, average particle diameter
of 16 .mu.m, minimum particle diameter of 7 .mu.m, maximum particle
diameter of 40 .mu.m, and specific surface area of 0.23
m.sup.2/g.
Example 5
[0100] This example is similar to Example 3 except that physical
properties of the positive electrode active material are different.
Specifically, LiCoO.sub.2 as the positive electrode active material
has, as shown in Table 2, average particle diameter of 22 .mu.m,
minimum particle diameter of 9 .mu.m, maximum particle diameter of
50 .mu.m, and specific surface area of 0.21 m.sup.2/g.
Comparison Example 3
[0101] This example is similar to Example 3 except that physical
properties of the positive electrode active material are different.
Specifically, LiCoO.sub.2 as the positive electrode active material
has, as shown in Table 2, average particle diameter of 6 .mu.m,
minimum particle diameter of 3 .mu.m, maximum particle diameter of
12 .mu.m, and specific surface area of 0.51 m.sup.2/g.
Comparison Example 4
[0102] This example is similar to Example 3 except that physical
properties of the positive electrode active material are different.
Specifically, LiCoO.sub.2 as the positive electrode active material
has, as shown in Table 2, average particle diameter of 8 .mu.m,
minimum particle diameter of 5 .mu.m, maximum particle diameter of
16 .mu.m, and specific surface area of 0.38 m.sup.2/g.
[0103] Examples 3 to 5 and Comparative Examples 3 and 4 fabricated
as described above were evaluated. Evaluation items are expansion
ratio and capacity sustain ratio.
[0104] First, the expansion ratio will be described. The expansion
ratio of a battery was measured as follows. A plurality of
batteries of the examples and the comparative examples were
prepared. Each battery was charged under the conditions of 4.2V,
500 mA, and two hours and thirty minutes, and the thickness of the
battery was measured. After that, the batteries were stored under
the conditions of constant temperature and fixed period such that
the batteries were stored at 23.degree. C. for one month,
35.degree. C. for one month, 45.degree. C. for one month,
60.degree. C. for one month, and 90.degree. C. for four hours. The
thickness of each of the batteries one hour after the end of
storage. A variation in thickness before and after the storage is
used as an expansion amount. The expansion ratio is defined as
follows.
Expansion ratio (%)=(expansion amount/thickness of a battery before
storage).times.100
[0105] The following method of measuring the thickness of a battery
was used. Specifically, the battery was placed on a stand having a
horizontal plane. A disc which is parallel to the plane and is
larger than the surface portion of a battery was lowered to the
battery. The thickness of the battery was measured in a state where
a load of 300 g was applied to the disc. When the surface portion
of the battery was not a flat face, the highest part of the surface
portion of the battery was used to measure thickness.
[0106] In FIG. 6, L=62 mm, W=35 mm, and D=3.8 mm. The device area
is 56 mm.times.34 mm=1904 mm.sup.2. When the surface portion of a
battery is a flat face, pressure to be applied on the battery is
0.16 gf/mm.sup.2.
[0107] The capacity sustain ratio will now be described. First,
each of the batteries was charged with constant current and
constant voltage of hour rate of 5 (0.2 C) for 15 hours to the
upper limit of 4.2V and discharged with constant current of 0.2 C,
and the discharge was finished at the final voltage of 2.5V. The
discharge capacity was determined in such a manner and was set as
100%. After charging batteries under the above-described charging
conditions, the batteries were stored under the conditions of
23.degree. C. for one month, 35.degree. C. for one month,
45.degree. C. for one month, 60.degree. C. for one month, and
90.degree. C. for four hours. The batteries were discharged under
the above-described discharging conditions. The charging and
discharging was repeated five more times. The discharge capacity at
the fifth time was measured and is displayed in % so as to be
compared with the discharge capacity of 100%. The capacity of 100%
in each of Examples 3 to 5 and Comparative Examples 3 and 4, that
is, the capacity before storage was almost equal to each other.
[0108] The results of measurement of the expansion ratio after
storage are as shown in Table 3. When the expansion ratio is 5% or
lower, there is no problem in practice. Consequently, the expansion
ratio of 5% was used as a reference of evaluation. As understood
from Table 3, Example 3 has the expansion ratio ranging from 0 to
5% and proves itself excellent. Example 4 has the expansion ratio
ranging from 0 to 3% and proves itself excellent. Example 5 has the
expansion ratio ranging from 0 to 2% and proves itself excellent.
In contrast, Comparative Example 3 has a high expansion ratio of 10
to 25% except for the condition of 23.degree. C. for one month.
Comparative Example 4 has a high expansion ratio of 9 to 20% except
for the condition of 23.degree. C. for one month.
6TABLE 3 Expansion ratio after storage Expansion ratio Comparative
Comparative Example 3 Example 4 Example 5 Example 3 Example 4
(average (average (average (average (average Condition particle =
particle = particle = particle = particle = Temperature Storage 10
.mu.m) 16 .mu.m) 22 .mu.m) 6 .mu.m) 8 .mu.m) 23.degree. C. one
month 0% 0% 0% 0% 0% 35.degree. C. one month 3% 2% 2% 10% 9%
45.degree. C. one month 3% 2% 2% 15% 12% 60.degree. C. one month 3%
3% 2% 20% 15% 90.degree. C. four hours 5% 3% 2% 25% 20%
[0109] It is understood from the above that the positive electrode
active material used for Examples 3 to 5 produces an excellent
result with respect to the expansion ratio. Specifically, in
Examples 3 to 5, the average particle diameter of the positive
electrode active material lies in a range from 10 to 22 .mu.m. The
positive electrode active material has the minimum particle
diameter of 5 .mu.m, the maximum particle diameter of 50 .mu.m, and
the specific surface area of 0.25 m2/g and less.
[0110] It is considered that the positive electrode active
materials in Examples 3 to 5 obtain excellent results with respect
to the expansion ratio for the following reason. The cause of
expansion of a battery when the battery is stored at high
temperature is regarded as generation of gas. The cause of the
generation of gas is considered that, due to contact between the
surface of the positive electrode active material with the
electrolyte solution, reaction occurs on the surface, and cracked
gas of CO.sub.2 or hydrocarbon generates. Since the surface area of
the positive electrode active material of each of Examples 3 to 5
is smaller than that of the positive electrode active material of
each of Comparative Examples 3 and 4, it is presumed that due to
the small surface area for reaction, decomposition reaction is
suppressed. As a result, the expansion of the battery based on the
cracked gas is suppressed.
[0111] The results of measurement of the capacity sustain ratio
after storage are as shown in Table 4. As understood from Table 4,
Example 3 has the capacity sustain ratio ranging from 94 to 98% and
proves itself excellent. Example 4 has the capacity sustain ratio
ranging from 96 to 98% and proves itself excellent. Example 5 has
the capacity sustain ratio ranging from 97 to 98% and proves itself
excellent. In contrast, Comparative Example 3 has a capacity
sustain ratio of 90 to 95% which is lower as compared with Examples
3 to 5. Comparative Example 4 has a capacity sustain ratio of 92 to
96% which is lower as compared with Examples 1 to 3.
7TABLE 4 Capacity sustain ratio after storage Capacity sustain
ratio Comparative Comparative Example 3 Example 4 Example 5 Example
3 Example 4 (average (average (average (average (average Condition
particle = particle = particle = particle = particle = Temperature
Storage 10 .mu.m) 16 .mu.m) 22 .mu.m) 6 .mu.m) 8 .mu.m) 23.degree.
C. one month 97% 98% 98% 95% 96% 35.degree. C. one month 96% 98%
98% 94% 95% 45.degree. C. one month 95% 97% 97% 92% 93% 60.degree.
C. one month 94% 96% 98% 90% 92% 90.degree. C. four hours 98% 98%
98% 90% 94%
[0112] It is understood from the above that the positive electrode
active material used for Examples 3 to 5 produces an excellent
result with respect to the capacity sustain ratio after storage.
Specifically, in Examples 3 to 5, the average particle diameter of
the positive electrode active material lies in a range from 10 to
22 .mu.m. The positive electrode active material has the minimum
particle diameter of 5 .mu.m, the maximum particle diameter of 50
.mu.m, and the specific surface area of 0.25 m2/g and less.
[0113] It is considered that the positive electrode active
materials in Examples 3 to 5 obtain excellent results with respect
to the capacity sustain ratio for the following reason. Since the
surface area of the positive electrode active material of each of
Examples 3 to 5 is smaller than that of the positive electrode
active material of each of Comparative Examples 3 and 4, it is
presumed that due to the small surface area for reaction,
decomposition reaction is suppressed. Due to reduction in the area
for reaction, speed of deterioration in the positive electrode
active material is also suppressed.
[0114] From the above, according to the second aspect of the
invention, the expansion which occurs when a non-aqueous gel or
solid electrolyte polymer secondary battery using a metal foil case
laminated electrical insulator material is stored at high
temperature and is a conspicuous problem in the secondary battery
can be suppressed. The discharge capacity sustain ratio can be
improved. Specifically, the positive electrode active material is a
composite oxide made of Li and other metal, and the average
particle diameter of the positive electrode active material lies
within the range from 10 to 22 .mu.m, the specific surface area is
reduced, the reaction area is decreased and, as a result, the
generation of gas is suppressed when the battery is stored at high
temperature. The expansion of a battery which occurs when the
battery is stored at a high temperature can be suppressed. Thus,
the discharge capacity sustain ratio can be improved.
[0115] Examples of a third aspect of the invention will be
described hereinbelow.
Example 6
[0116] (Fabrication of Positive Electrode)
[0117] Suspension of the following composition of the positive
electrode active material layer was mixed by a disper for four
hours and was coated in a pattern on both sides of aluminum foil
having a thickness of 20 .mu.m. The coating pattern includes a
coated portion having a length of 160 mm and an uncoated portion
having a length of 30 mm, which are repeatedly provided on both
sides. The start and end positions of coating on both sides were
controlled to coincide with each other.
8 Composition of positive electrode active material layer parts by
weight LiCoO.sub.2 (average particle diameter: 10 .mu.m) 100
polyvinylidene fluoride 5 (average molecular weight: 300,000)
carbon black (average particle diameter: 15 nm) 10
N-methyl-2-pyrrolidone 100
[0118] The above-described positive electrode active material
LiCoO.sub.2 contains one part by weight of lithium carbonate
(Li.sub.2CO.sub.3).
[0119] The positive electrode active material LiCoO.sub.2 contains
400 ppm of moisture. The moisture in the positive electrode active
material LiCoO.sub.2 was reduced to 400 ppm by drying the positive
electrode active material LiCoO.sub.2 in vacuum and controlling the
drying time.
[0120] Quantitative analysis of the moisture was conducted as
follows. 0.5 g of the sample of the positive electrode active
material was extracted and heated at 250.degree. C. to vaporize the
moisture, and the content of moisture was measured by a Karl
Fischer measuring apparatus.
[0121] Quantitative analysis of the content of lithium carbonate
was made as follows. 2.0 g of the positive electrode active
material was extracted, and analyzed by using the A.G.K. CO.sub.2
analysis method (titration method described in JISR9101).
[0122] Although the moisture is also contained in other materials
such as the negative electrode material, gel, electrolyte, the
moisture contained in each of them is very little. The moisture
existing in a battery can be therefore determined by controlling
the moisture contained in the positive electrode active
material.
[0123] The row sheet of which both sides were coated with the
positive electrode was pressed with linear pressure of 300 kg/cm.
After the press, the thickness of the positive electrode was 100
.mu.m and the density of the positive electrode active material
layer was 3.45 g/cc.
[0124] (Fabrication of Negative Electrode)
[0125] Suspension of the following composition of the negative
electrode active material layer was mixed by a disper for four
hours and was coated in a pattern on both sides of copper foil
having a thickness of 10 .mu.m. The coating pattern includes a
coated portion having a length of 160 mm and an uncoated portion
having a length of 30 mm, which are repeatedly provided on both
sides. The start and end positions of coating on both sides were
controlled to coincide with each other.
9 Composition of negative electrode active material layer parts by
weight artificial graphite 100 (average particle diameter: 20
.mu.m) polyvinylidene fluoride 15 (average molecular weight:
300,000) N-methyl-2-pyrrolidone 200
[0126] The row sheet of which both sides are coated with the
negative electrode was pressed with linear pressure of 300 kg/cm.
After the press, the thickness of the negative electrode was 90
.mu.m and the density of the negative electrode active material
layer was 1.30 g/cc.
[0127] (Formation of Gel Layer Containing Electrolyte Solution)
[0128] The composition for forming the gel layer containing the
electrolyte solution was mixed by a disper for one hour in a heated
state at 70.degree. C. and was coated in a pattern on the negative
electrode active material layers on both sides of the negative
electrode collector so as to have a thickness of 20 .mu.m and was
coated in a pattern on the positive electrode active material
layers on both sides of the positive electrode collector so as to
have a thickness of 20 .mu.m. A dryer was controlled so that only
dimethyl carbonate evaporates substantially.
10 Composition for forming gel layer parts by containing
electrolyte solution weight poly(hexafluoropropylene-vinylidene
fluoride) copolymer *1 5 dimethyl carbonate (DMC) 75 electrolyte
solution (LiPF6: 1.2 mole/litter) *2 20 *1: content of
hexafluoropropylene = 6 parts by weight *2: solvents used for
electrolyte solution: ethylene carbonate (EC)/propylene carbonate
(PC)/.gamma.-butyrolactone (GBL) = 4/3/3
[0129] At the time of forming the gel layer containing electrolyte
solution, the positive and negative electrodes were heated by
setting an electrode preheater at a predetermined temperature of
60.degree. C.
[0130] The row negative electrode on which the gel layer containing
the electrolyte solution was formed, was cut into 40 mm width to
fabricate a negative electrode band. The row positive electrode was
cut into 38 mm width to fabricate a band-shaped positive electrode
body.
[0131] (Fabrication of Battery)
[0132] After that, the leads were welded to both the positive and
negative electrodes, and the positive and negative electrodes were
adhered to each other so that their electrode active material
layers were in contact with each other and contact-bonded. The
resultant was sent to an assembling section where the battery
device was formed. The battery device was sandwiched so as to be
covered with the metal laminated films. By welding the metal
laminated films, the non-aqueous gel polymer secondary battery as
shown in FIG. 6 was fabricated. As described above, the non-aqueous
gel polymer secondary battery of the embodiment uses an aluminum
laminate case. The metal laminated film was obtained by stacking
nylon, aluminum, and casting polypropylene (CPP) in accordance with
the order from the outside. The thickness of nylon is 30 .mu.m,
that of aluminum is 40 .mu.m, and that of CPP is 30 .mu.m. The
thickness of the whole stack layers is 100 .mu.m.
Examples 7 to 21
[0133] Examples 7 to 21 are similar to Example 1 except for the
contents of the lithium carbonate and moisture in the positive
electrode active material.
[0134] Specifically, the content of lithium carbonate in each of
Examples 7 to 9 is 1 part by weight. The contents of moisture of
Examples 7 to 9 are 300 ppm, 200 ppm, and 100 ppm,
respectively.
[0135] The content of lithium carbonate in each of Examples 10 to
13 is 0.15 percent by weight. The contents of moisture of Examples
10 to 13 are 400 ppm, 300 ppm, 200 ppm, and 100 ppm,
respectively.
[0136] The content of lithium carbonate of each of Examples 14 to
17 is 0.07 percent by weight. The contents of moisture of Examples
14 to 17 are 400 ppm, 300 ppm, 200 ppm, and 100 ppm,
respectively.
[0137] The content of lithium carbonate of each of Examples 18 to
21 is 0.01 percent by weight. The contents of moisture of Examples
18 to 21 are 400 ppm, 300 ppm, 200 ppm, and 100 ppm,
respectively.
[0138] Examples 6 to 21 fabricated as described above were
evaluated. Evaluation item is an expansion ratio. The expansion
ratio will now be described. The expansion ratio was measured as
follows. First, each of the batteries in the examples was charged
under the conditions of 4.2V, 500 mA, and two hours and thirty
minutes, and the thickness of the battery was measured. After that,
the batteries were stored at 90.degree. C. for four hours. The
thickness of each of the batteries one hour after the end of
storage was measured. A variation in thickness before and after the
storage is used as an expansion amount. The expansion ratio is
defined as follows.
Expansion ratio (%)=(expansion amount/thickness of a battery before
storage).times.100
[0139] The following method of measuring the thickness of a battery
is used. Specifically, the battery is placed on a stand having a
horizontal plane. A disc which is parallel to the plane and is
larger than the surface portion of a battery is lowered to the
battery. The thickness of the battery was measured in a state where
a load of 300 g was applied to the disc. When the surface portion
of the battery is not a flat face, the highest part of the surface
portion of the battery is used to measure thickness.
[0140] In FIG. 6, L=62 mm, W=35 mm, and D=3.8 mm. The device area
is 56 mm.times.34 mm=1904 mm.sup.2. When the surface portion of a
battery is a flat face, pressure to be applied on the battery is
0.16 gf/mm.sup.2.
[0141] The result of measurement of the expansion ratio after
storage is as shown in Table 5. When the expansion ratio is 4% or
lower, there is no problem in practice. It is therefore desirable
that the expansion ratio is 4% or lower.
11TABLE 5 Expansion ratio of battery Li.sub.2CO.sub.3 (percent by
weight) 1 0.15 0.07 0.01 moisture 400 9.00% 6.80% 6.00% 4.70% (ppm)
300 7.50% 4.00% 3.60% 3.00% 200 6.40% 3.50% 2.80% 2.40% 100 5.10%
2.80% 2.30% 2.00%
[0142] 4% of the expansion ratio is applied to the range where the
content of lithium carbonate is 0.15 percent by weight, and the
content of moisture is 300 ppm and less.
[0143] As described above, by controlling the contents of lithium
carbonate and moisture in the positive electrode active material,
the expansion ratio of the battery can be suppressed to 4% or
lower. The reason that the expansion ratio decreases is considered
as follows. In the case where lithium carbonate is contained in the
positive electrode active material, the lithium carbonate is
decomposed by heat when the battery is stored at high temperature
and carbon dioxide is resulted. When moisture exists in the
positive electrode active material, reaction occurs between the
moisture and an electrolyte such as LiPF.sub.6 to generate HF. By
the action of HF, the decomposition of lithium carbonate is
promoted, and carbon dioxide is generated. The generation of carbon
dioxide is considered as a cause of the expansion of a battery. In
the embodiment, the contents of lithium carbonate and moisture as a
cause of generation of carbon dioxide are reduced. Consequently, it
is presumed that occurrence of carbon dioxide is suppressed, and
the expansion of a battery is accordingly suppressed.
[0144] In consideration of the above, according to the third
embodiment of the invention, the positive electrode active material
is a composite oxide of Li and a transient metal, and carbonate
contained in the positive electrode active material is equal to or
lower than 0.15 percent by weight. Consequently, decomposition
reaction when the battery is stored at high temperature is
suppressed. Thus, expansion of the battery when the battery is
stored at high temperature can be suppressed.
[0145] Although not specifically described here, similar effects
are also produced also in the case where other laminated films
having structures other than the structure in which a nylon film,
aluminum foil, and a polyethylene film are sequentially laminated
are used. Similar results can be obtained also in the case where a
metal film or a polymer film is used in place of the laminated
film.
[0146] Although the invention has been described by the foregoing
embodiments and examples, the present invention is not limited to
the embodiments and the examples but can be variously modified. For
example, although the secondary batteries each using a gel
electrolyte containing lithium salt, a non-aqueous solvent, and a
polymer material has been described in the embodiments and
examples, in place of the gel electrolyte, other electrolytes such
as a liquid electrolyte obtained by dissolving a lithium salt into
a solvent, a solid electrolyte obtained by dispersing lithium salt
into polyethylene glycol or a polymer compound having ion
conductivity such as acrylic polymer compound may be used.
[0147] In the foregoing embodiments and examples, the two films 30a
and 30b are used as the packaging member 30 and the battery device
20 is sealed in the two films 30a and 30b. It is also possible to
fold a single film, closely adhere the peripheries of the film, and
seal the battery device 20 in the folded film.
[0148] Further, the secondary batteries have been described as
specific examples in the foregoing embodiments and examples. The
present invention can be also applied to batteries of other shapes
as long as a film-state packaging member is used. In addition,
although the non-aqueous secondary batteries have been described in
the foregoing embodiments and examples, the present invention can
be also applied to other batteries such as primary battery.
[0149] As described above, in the battery of the invention, the
concentration in mass ratio of a free acid in a non-aqueous
electrolyte is suppressed to 60 ppm. Consequently, generation of a
gaseous hydride in a battery and generation of a gas due to
corrosion reaction in the battery can be suppressed. Thus, even
when a film-state packaging member is used, effects such that a
change in shape due to expansion can be prevented and the shape can
be maintained even when the battery is stored in a high-temperature
environment.
[0150] It is also possible to suppress consumption of an electrode
reactant due to reaction between the free acid and an electrode
reactant in a battery system. An effect such that deterioration in
battery characteristics can be prevented is also produced.
[0151] The second aspect of the invention produces effects such
that, since the positive electrode active material is a complex
oxide of Li and transition metal, and the average particle diameter
of the positive electrode active material lies in the range from 10
to 22 .mu.m, the expansion of the battery when the battery is
stored at high temperature can be suppressed. The discharge
capacity sustain ratio can be also improved.
[0152] The third aspect of the invention produces effects such
that, since the positive electrode active material is a complex
oxide of Li and transition metal, and carbonate compound contained
in the positive electrode active material is 0.15 percent by
weight. Thus, expansion of a non-aqueous electrolyte battery which
occurs when the battery is stored at high temperature can be
suppressed.
[0153] Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced other wise than as
specifically described.
* * * * *